1. Field of the Invention
The invention relates to a method and apparatus for drying organic material. More particularly, but not exclusively, the invention relates to a method of extraction/distillation of aqueous solutions and secretions from organic mass and/or the drying of such organic mass and to apparatus for carrying out the same.
2. Discussion of the Background
Many materials used in commerce and industry derive from plants which grow in nature and contain many complex substances required by the plant to fulfil a wide range of functions.
Organic materials are used to produce many products for commerce and industry especially, but not exclusively, in the food and drink industries, and the processes used create by-products which comprise the residues of organic materials after certain fractions such as juice, pulp, seeds or skin have been used to make commercially desirable products from organic feedstock.
These residues are putrescible and they therefore present a significant waste disposal problem. They require disposal within a few hours or days of the initial processing operation and the products of decomposition may produce polluted leachate running into aquifers and noxious substances and odours emitted to atmosphere unless they are subject to disposal under careful and expensive conditions to prevent such pollutions of aquifers and atmosphere.
Plants also provide the feedstock for many bactericidal, fungicidal, cleaning, pharmaceutical, veterinary, flavours, perfumery and other consumer products as well as for the human food and drink and animal feed industries.
Where solid fractions are required for use as feedstocks in a process, these are normally obtained by drying which is a process in which moisture is driven off to atmosphere by the application of heat. This may or may not be subject to filtration of flue gases which are normally contaminated with evaporated liquids mixed with products of combustion of the fuel.
Where liquid fractions are required for use as feedstocks in a process, these are normally obtained by distillation which is a process in which moisture is driven off by the application of heat and is collected after condensation, with the solid residues normally being discarded as waste by-products. There is an opportunity to improve economy by combining the processes.
Desire to minimise damage to the global environment has led to a growing interest amongst peoples throughout the world in the possibilities of replacing synthetic substances, which are often derived from non-replaceable fossil fuel origins, with "natural" products. Such synthetic substances which can be of limited availability are being used up at a significantly fast rate.
All, or virtually all, plants secrete some oils or other liquids which are held in special oil glands, in sacs or in intercellular spaces of the plant tissue. These secreted substances are normally virtually insoluble in water and normally immiscible with water. They normally remain in the organic mass of plants when moisture is drained or driven off at low or medium temperatures. Many of these secreted substances have a high value for commercial usage.
During the life of the plant these secretions may be held or released for a variety of purposes. including, perhaps, such uses as attracting insects for pollination; repelling animal predators or dissuading parasites; repairing wounds; cooling by varnishing or vaporisation of oils; colouring; supplementing food reserves and many other such functions. These secretions are frequently oils in which case they may be known as essential, volatile or ethereal oils. If they are not oils, they may be alcohols, esters, ketones, aldehydes, terpenes, steroids, resins, latexes, rubbers, anthrocyanines, flavones and many other such substances. For the purposes of this application, all of the above will be referred to for convenience as essential oils. The common grouping derives from the combined qualities that they are largely insoluble with water and immiscible with water and that the plant secretes them away from its main tissue which contains large percentages of aqueous solutions or juices.
It is becoming more and more accepted in current commercial thinking that many of these secreted substances have importance to humans for a wide variety of commercial purposes.
Many new pharmaceutical and veterinary products are now and will be increasingly in the future derived from substances which are, themselves, derived from the secretions of plants as well as foods, drinks, flavours, perfumes and household goods for which they have been commonly used for centuries past.
Most of these secreted substances evaporate at temperatures of 150 to 300 degrees centigrade, well above the temperature at which water evaporates, namely 100 degrees centigrade. If however, these are evaporated in circumstances in which water and the secreted substances behave as a two phase liquid/two phase vapour, then the boiling point may drop to become lower than either of the constituents in their own right. Thus extraction of high boiling point substances is aided when a two phase liquid is evaporated from an organic mass. The issue to be resolved in such a circumstance is to remove the inaccessible secreted substances from the gland or sac in which they are held. Migration of such substances does not normally occur at the boiling temperature of water. For centuries past, distillation of secreted substances has required the application of superheated steam at temperatures capable of bursting the gland or sac which contains the secretion. The background to the invention includes the concept of bringing this past practice into the fields of waste recycling and animal food production.
Recently, there has been an unusually large increase in the cost of disposal of many organic wastes which are the by-products of manufacturing processes, most especially putrescible wastes that derive from organic feedstocks. The concept known as "The polluter must pay" has led, throughout the world, to a review of historic methods of disposal, principally "Landfilling", which involves placing waste into a hole in the ground. Political pressures everywhere are requiring higher standards of sealing landfill holes from aquifers and the atmosphere. This adds to expense.
Taxation is increasingly being used to direct commercial organisations down a recycling route instead of the landfilling route and many environmental groups actively promote recycling as desirable.
These circumstances have raised interest in new inventions which can make positive value products from what have been considered negative value costs of disposal. To achieve this any recycled products must be of marketable quality and fit for sale without fear of infections and contamination. One factor here is sterility and any process involving biodegradable substances and substances which may provide nutrients for organisms to grow must be put through a process which gives them sufficient time in the "Pathogen kill zone" of temperatures to ensure sterility of the finished product. A process which requires the feedstock to be subjected to many minutes at superheated steam temperatures in excess of that experienced in hospital autoclaves, for example, becomes particularly desirable when organic wastes are recycled.
The coincidence of increased interest in the beneficial properties of secreted substances from plants coupled with increased interest in cleaning the environment makes this an appropriate time to introduce an invention which contributes to both objectives in an integrated method and apparatus. Initial work carried out on citrus residues in order to produce marketable recycled products has a much wider application for obtaining both solid and liquid marketable quality products from either organic wastes or freshly cropped plants.
An example of the coincidence of demand for secreted substances and environmental pressure arises from the need to deal with the by-products of products which have been actively developed recently, namely freshly squeezed orange, grapefruit or lemon juice, produced in a factory and distributed through supermarket chains that same day. Having squeezed out the juice, the remainder of the fruit is normally discarded. After this, it is disposed of, either by tipping into landfills or by spreading on fields for animal consumption.
The first of these processes is becoming increasingly expensive, if pollution of aquifers and the atmosphere is to be avoided, and the second is now normally prohibited. The citrus residue decomposes rapidly, causing airborne smells and pollution of aquifers via road drainage during transport and via field drainage if it is spread in fields for animal consumption. The presence of the most common secreted substance in citrus residues, d-limonene, makes such waste relatively unpalatable to many ruminant animals which are conversely attracted to consume the dried material when the d-limonene is largely removed. The d-limonene however, is itself a valuable commercial product for flavour enhancement of food products and in many other uses.